Case control study examining the role of livestock markets in the transmission of bovine tuberculosis

Mycobacterium bovis infection in cattle is mainly a respiratory disease with airborne infection being the principal route of transmission (O'Reilly & Daborn, 1995). Infected cattle and the European badger (Meles meles) are the major sources of infection for cattle in Great Britain and Ireland, although the relative significance of each has not been clarified (Krebs, 1997). This study examined one potential factor in bovine-bovine spread, namely the movement patterns of cattle. The purpose was to assess if any significant difference could be detected between the movement frequency of cattle with confirmed tuberculosis (TB) and that of selected control animals. Lifetime movement history was assessed, in particular, movement through markets. The extent of contact between reactors within a market on the same day was calculated and compared to that of the control group.

Extensive use was made of the animal health database maintained by the Department of Agriculture and Rural Development in Northern Ireland. This was established in 1988 and holds animal and herd details of all cattle in the province as well as their TB-test and movement history. Department staff issue permits to authorise movement of cattle between herds or onto other premises, such as livestock shows and abattoirs. Computer terminals, based in markets and abattoirs, are used by Animal Health Inspectors to check the details and status of all incoming cattle and to issue outbound permits from markets to specified destinations. Such checks, together with the herd audit provided by annual TB testing of all herds, has resulted in a comprehensive database of animal movement history. Each animal can be traced from birth to death and the health status of each herd checked, including intermediate herds. Furthermore, forward and backward tracing of cattle from infected herds can be initiated immediately infection is disclosed, facilitating the rapid identification and testing of suspect cattle.